Transmission system for television signals



SPt 15, 1959 J; HAANTJES ET AL 2,904,628

TRANSMISSION SYSTEM FOR TELEVISION SIGNALS J OHAN HAANTJES K EES TEERSept. 15, 1959 J. HAANTJES ETAL TRANSMISSION SYSTEM FOR TELEVISIONSIGNALS Filed Jan. 26, 1956- 3 Sheets-Sheer. 2

FIGA

FIG7

NVENTOR JOHAN HAANTJES KEES TEER sept. 15, 1959 Filed Jan. 26, 1956 J.HAANTJES I'AL TRANSMISSION SYSTEM FOR TELEVISION SIGNALS 3 Sheets-Sheet3 all-1l lNVENTOR JOHAN HAANTJEs KEES TEER United States Patent()TRANSMISSION SYSTEM FOR TELEVISIN SIGNALS Johan Haantjes and Kees Teer,Eindhoven, Netherlands, assignors, by mesne assignments, to NorthAmerican Philips Company, Inc., New York, NSY., a corporation ofDelaware i ApplcationJanuary 26, 1956, Serial No. 561,627

Claims priority, application Netherlands February 10, 1955 3 Claims.(Cl. 178-6) Y The invention relates to a transmission system forVV:signals 'corresponding to television images or similar imageswhich'are scanned linewise,'in which moreover at least one auxiliarycarrier wave, modulated by signals also corresponding to similar images,is transmitted, and also relates to such a system in which noinformation need be transmitted from the transmitter to the receiver forthe demodulation of the signals modulated on the auxiliary Carrier Wave'Such systems may be used for colour television. An example ofV such asystem is one in which a signalof "large bandwidth is transmittedcontinuously, whilst two other `sigfnalslof smaller bandwidth',modulated Aon the same lauxiliary carrier wave,aie transmittedalternately. Y A' further example is a system inwhich asign'all of'largebandwidth is transmitted continuously, whilst two other signals ofsmaller bandwidth modulated leach ona sepavrate auxiliary carrier, aretransmitted Yalso continuously."

In such systems it suicesat the receiver end for'the demodulation ofthesignals modulated on an auxiliary carrier'to use; al bandpass filter anda detector circuit y`witl 1"ofl'1t'the need Yfor vflrther informationfrom the "transmitter at the detector.A This information is,`on the"contrary, lrequired, if the two signals of smaller band- `widthare'modulated in quadrature onl an vauxiliaryfcar- `rier; For thedetection the receiver then requirestwo auxiliary oscillations, thefrequencies of which correspond tothose of the auxiliary carrier, aparticular phase*4 'relationship prevailing between'V theseauxiliaryoscilla- `rtions and theY auxiliary carrier. In order to obtainthe said frequency equality and the said phase relationship between theauxiliary oscillations produced in thefreceiver and the auxiliarycarrier produced in the'trans-V mitter the transmitter emits furtherinformation about `this auxiliaryV carrier. VIn a 'knolwn system thisfurther f information consists in a reference signal (colour burst),

"the frequencyof which corresponds tothat of the aux-- Such referencesignals withv the correct frequency `and`v` ythe correct phaseare notrequired for `the demodulation of -vthe auxiliaryv carrier inthe'systems to`which the Svinvention applies. In accordance withthe'invention it is, `l1o`wever,` to be" preferred to transmitsimultaneously reference signals, 'be it for quite different reasons,whilst,

' on-the'lother hand, a correctphase relationship between thesereference signals andthe auxiliary carriers produced in the transmitteris quite irrelevant. 'i i" 'I'hisre'ason will be explained more fullyhereinafter.

`A colour television transmitter emits, Withthe 'aid of"4 a main carrieror without it, a signal'of large bandwidth'and, for example, two signalsof smaller'band- `-widtl1modulated yeach ono'ne auxiliary carrier. 'Thesignal of large bandwidth'ma'yibe Ia lbrightiless"'jsignal "and 'thetwosignals of smaller bandwidth may be colourn 2,904,628 Patented Sept. 15,1.959

ICC

signals. The frequencies of the auxiliary carriers lie either outsidethe frequency of the band ofthe signal of large bandwidth or inside thisfrequency band, where the higher frequencies of the signal of largebandwidth 5 lie. It is known that the signals to be finally fed to thepicture tube or tubes are, as a rule, formed by combining in aparticular ratio the three signals thus transmitted. For a truereproduction of the scene converted into television signals at thetransmitter end it is, of course, desirable for the amplitudes of thethree transmitted signals to maintain their same ratio to one another atthe beginning and at the end of the transmission path. lf it is assumedthat the scene to be reproduced is a white plane and that, for somereason or other the amplitude of the colour signal relating to the bluelight components of the scene to be reproduced is reduced to zero, theimage finally reproduced at the receiver end will represent a yellowplane. The fact that the signal relating to a colour component iscompletely suppressed, is, of course, an extreme case, but

it will be obvious that any linear distortion in the transmission path,rfor example selective fading and frequencydependent reflection in thecase of a transmission with the aid of a carrier Wave or afrequency-dependent transmission characteristic in the case of atransmission via a cable, does not contribute to the desired truereproduction. l The system according to the invention obviates thesedisadvantages and has the feature that a reference signal is supplied tothe transmission path at the transmitter end during'fthe occurrence ofthe backporches of the line 'synchrohizing pulses, the amplitude of thisreference 4`signal being'constant, its frequency corresponding at leastsubstantially to"the`"frequency of an auxiliary carrier and "that atthereceiver end provision is made of means which Ifcor'itrol'- theamplification factor of the transmission path "iwithinthereceiver-forthe signal modulated on the aux- -"i1iary` carrierfin accordance withthe amplitude of the associated reference signal. e 40 VlThe inventionwill be Idescribed more fully with refer- Itence 'tofthe ligures'ofthefdrawing, in which a Fig. l shows the frequency spectrum of threetelevision 'signals Tin the transmission f path with al' system"according ato* the'fmveom- .i' f =t .f :'1'-, g. Figf Zlshows thefrequency spectrum -`of`theselthree s gnals at the transmitter ed.-FgfSshows dagranmaticallyan vemljodir'nen of' a V'transmitter for use^ fin a system *according -toV th'f invention. 't 'f- Figs.4, 5, 6 and 7show signal forms liable to occur in a system according to theinvention. "Fig, 8 shows also diagrammatically one embodiment of atransmitter for use in a system acording to' the *invention i Y p 55'Fig. 9 'shows diagrammatically one embodimentof a ireceiver for use in asystem according to the invention and Fig. 10 'shows a circuitarrangement for use in`the receiver shown in Fig. 9. v v

Fig.1 shows an example-of a frequency spectrum Aoccurring in a colourtelevisionsystem according to the invention. Such a'frequcncy spectrum,which extends from a frequency fd-fe to a frequency fd-I-fa, is producedby the modulation of a carrier wave of the frequency fd by threesignals, of which the rst extends in a frequency band from 0 to fa, thesecond extends from fb to fc the third extends from fg to fk, asindicated in Fig. 2,and the lower sideband being partly suppressed. 'Ihesignal of large bandwidth mayy be, fr example, the brightness signal;the second signal between the frequencies fl, and fc is produced bymodulating an auxiliary carrier ofthe frequency fm by one of the coloursignals; the third f most to a `satisfactory result.--visiQn-,transmission .by means of a system according to required.

function of time.

3 signal between the frequencies fg and fk is produced by modulating anauxiliary carrier of the frequency fm by the other colour signal. Theauxiliary carriers have, of

,course,v such frequencies and, as the case may be, such phase.,differences that the relative interference of the varioussignals issubstantially imperceptible to the eye A ,at the reproduction.

v Such -a frequency spectrum is, of course, also produced by modulatinga carrier ofthe frequency fd by the signal ,of large -bandwidth and bymodulating each of two carriersvof4 Afrequenciesfd-l-lhl and fd-.l-fhzby a colour signal. Subsequent todemodulation in the receiver, however,the

carriers fd-l-fhl and fall-12,2 appear yet again in the video frequenCyrSpectrum of the signal of large bandwidth as vauxiliary carriers of thefrequencies fm and fhg.

It is ,known that, as a rule, the attenuation of the signalcomposed-bythe carrier modulated bythe aforesaid three 'signalsy duringthe transmission path from the transmitter tofithe lreceiver will varywith time for reasons known per se. This-may even be the case in partsof the transmission path,fin the transmitter and in the receiver itself,

.owing to variations oftube characteristics and so on.

vfrequencies in the proximity of the carrier, in this case,

the low frequencies of the brightness signal, are maintainedat thedesired level. With a monochrome trans- ;mission this appears to belittle disturbing in practice in view of the fact that the lowerfrequencies contribute In the case of colour tele- 4the invention thecolour -information is transmitted in a V,frequency range which iscomparatively remote from the frequency range in which the said levelcontrol operates .-eciently. AIt will be obvious that this may give riseto images which deviate materially from the images wanted.

Inaccordance withfthe invention, a reference signal lis supplied to thetransmission path at the transmitter end during the occurrenceof ltheback-porches of the line synchronizing pulses, the amplitudeof thisreference sig- --nal beingconstant Vand its frequency correspondingatleast -foruse in a transmission systemy according to the invention is ablock diagram. The device 1 produces the brightness. signal and the twocolour signals at the outputs v,2,13 and 4. The device Il comprises,ltothis end,the required recording cameras and the arrangement further Inthe `device-5 the line and frame synchronizing pulses are produced.These-pulses aresupplied both to the device 1 to control the deflectionmeans of the -recording cameras and to the adding device 6, to which isalso-supplied the brightness signal occurring atv the output -2.

The `well-known shape of the signal thus occurring at the output ofdevice 6 is indicated partly in Fig. 4 as a Reference p designatesherein the line synchronizing pulses, V0 designates the black level. V0is a constant value. The line synchronizing pulses occur during.theperiods tp, the front porches of the black level occur duringthe-periods tv and the backporches of the .black level occur .dur-ingthe periods ta. The frame synchronizing pulses, the equalization pulsesand so on are not shown in this figure.

Fig. 5 shows the shape of an output signal occurring at the outputs 3 or4. From the figure it is evident that the amplitude of such a signal isreduced to zero during the periods tv-l-rp-l-ta. Each of the outputsignals occurring at the outputs 3 and 4 is supplied to an adding device8 and 7 respectively, to which is also supplied the output signal of thedevice 9. The device 9 supplies control pulses of the same repetitionfrequency as the line synchronizing pulses, however they are narrowerthan the line synchronizing pulses and are, at the same time, delayedrelatively to the latter, to an extent such that they occur yduring partof each of the periods ta. The device 9 is preferably synchronized, forexample, by the line synchronizing pulses from the device 5. The outputsignal of the adding devices 7 or 8 thus has the shape indicated in Fig.6. The output signalsof the devices 7 and f5 are supplied each to amodulator 10 and E l respectively, to which is also supplied anauxiliary carrier of the frequency fm and fhz respectively. lTheseauxiliary carriers originate from the devices l2 and 13, which compriseoscillators suitable for this purpose. With a View to the aforesaidchoice of the frequency and the phase difference thus occurring, if any,to yavoid relative interference of the various signals during thereproduction, these devices 12 and i3 are controlled by the lineor framesynchronizing pulses from the .device 5'. The output signal of themodulator l0 is fed to a bandpass filter ld having a pass range betweenthe frequencies fb and fc; the output signal of the modulator vlll isfed to a bandpass lter 15 having a pass range between the frequencies fpand fk. The output signals of the adding device 6, the bandpass iilter14 and the bandpass lilter l5 are combined in the adding device f6. Theoutput signal of the adding device 16 thus has the shape indicated inFig. 7. The signal portion occurring the periods tb is constituted bythe superimposition of the pulses indicated in Fig. 6, modulated on theauxiliary carrier of the frequency fm and these pulses modulated on theauxiliary carrier of the frequency fm. Similarly, the signal portionoccurring during the periods ts, is constituted by the superimpositionof the brightness signal and the two modulated colour signals.

'Ille output signal of the `device 16 is then fed to a low-pass lter 17,having a cut-olf frequency fa, and then combined in the adding device 18with the sound signal modulated on a carrier of the frequency fs. Thismodulated sound signal initiates from a device 19, which kcomprises tothis end the required microphones, amplifiers, modulators and so on.

The output signal of the device 1S may be transferred either to atransmission cable or, `as is indicated in the figures, to a modulator20, wherein the said signal is modulated on a carrier furnished by adevice 21, the frequency of this carrier being-fd, after which thesignal thus obtained is supplied to bandpass filter 22, having a passrange between the frequencies fd-fe and fd-l-ft (vide Fig. l) and thento a transmitter aerial23.

The introduction of the reference signals may, of course, be performedalsol in a `different way. Fig. 8 shows a simplied embodiment of atransmitter used in a 4transmission system according tothe invention inablock diagram, wherein a different method is used to introduce thereference signals. The corresponding parts of Figs. 3 and 8 aredesignated by the same reference numerals. In this embodiment thesignals occurring at the outputs 3 and 4 are fed directly to themodulators 11 and 10 respectively. The output signal of the device 9 ismodulated in two different modulators 24 and 25 on the auxiliarycarriers from the devices l2 and 13. The output signals of thesemodulators may, for example, be supplied also to the adding device 16,as well as the output signals of the devices 6, 14 and 15.

9 shows a simplified embodiment of a receiver Vin a block diagram, thisreceiver being suitable for the mixing stage 33' is `fed to anintermediate-frequency ampli- `Qfier34, which is coupled witha-detector`35 and a video .amplifier 36.

The carrier, modulated by the sound signal, may be lseparated from thetelevision signal `in -the intermediatefrequency stage 34 or in thedetector 35, according as use is made or not made oftheintercarrier-wave principle, and be supplied to anintermediate-frequency stage 41,.which is coupled with a sound detector42. The

output signal of the detector 42 -is fed via a low-frequency KHamplifier43 to one or more loudspeakers 44.A In Fig. 9

the sound carrier is shown separated from thetelevision in theintermediate-frequency stage 34.

The 4synchronizing signals contained in the output sigl nal of the videoamplifier 36 are regained from this output signal in the separatingcircuit 37.

'Ihe synchronizing pulses for the vertical deflection are fed yto thedevice 38 to synchronize the sawtooth generator forming part thereof;the output currents of 38 are fed to y the vertical deflecting coils(not shown) of the various i 'reproducing tubes. v r

The synchronizing pulses for horizontal deflection` are fed to thedevice 39 to synchronize the sawtooth generator forming part thereof;the output currents lfrom 39 are fed to the horizontal deflecting coils(not shown) of the reproducing tubes.

These devices 38 and 39 comprise moreover any required fly-wheelarrangements, whilst, moreover, from the device 39 a direct voltage maybe obtained in known manner from the fly-back of the line sawtoothgenerator, which direct voltage may be used as a high tension for `thepicture tubes.

For the conventional gain control the fly-back pulses from the device 39may be fed in known manner to a device 50, to which is also fed theoutput signal of the video amplifier 36. The device 50 comprises a gatecircuit, which becomes conductive under the action of the `said fly-backpulses only during the occurrence of the lineand frame-synchronizingpulses. The pulses at the output of the gate circuit, the amplitudes ofwhich pulses are proportional to the corresponding peak values of thesynchronizing pulses, are a measure for the level of the signaloccurring at the output of the video amplifier 36. The pulses thusobtained may be fed via smoothing networks 51 and 52 as control-voltagesto the highand intermediate-frequency stages.

As has been stated, this control has the disadvantage that, indeed, onlythe low frequencies of the signal occurring at the output of theamplifier 36 are brought to the correct level, which does not apply tothe frequencies lying in the range between fb and fc and between fg andfk, yi.e. those frequencies which relate to the colour information.

The output signal of the amplifier 36 is also fed to a bandpass filter53 having Ia pass range between the frequencies fb and fc and to abaudpass filter 54, having a pass range between the frequencies fg andfk. The output signals of the filters 53 and 54 are fed to the detectors55 rand 56 respectively, at the output of which occur, consequently,signals, the shape of which is shown in Fig. 6, these signals thuscontaining the reference signals occurring during the periods tb.

The devices 55 and 56 are connected to video amplifiers 57 and 58. Theoutput signals of the video amplifiers 36, 57 and 58 Vare fed to adevice 59, which comprises suitable, known combination networks. At theoutputs 61, 62 and 63 of the device 59 occur signals which relate `tothe red, green and blue components respectively-lof the scene to bereproduced. These signals may be-supplied to the control-elements ofreproducing tubes 64,

l 65 and 66, which reproduce thesel signals in red, green and blue lightrespectively. The signals may, of course,

"also be applied to the control elements of a single threecolourreproducing tube comprising three electron-guns.

vIf use is made of a three-colour reproducing tube comprising oneelectron gun, the signals must be 'applied` to the control-element ofthis tube in a particular succession of time. f

Any phase displacements of the various signals relative to one anotherhave so far not been considered; these phase shifts may be compensatedin known mannenfor example with the aid of delay-lines. z

The output signals of the amplifiers 57 and 58i'are fed to devices 70and 71 respectively, both of which comprise-a gate circuit and towhichthe output signals of a device 72 are supplied. For the sake ofcompleteness it is stated that in the circuits between the detectors 155and 56 on the one hand and the devices 70 and 71.0n

the other hand the direct current component must not get lost. Thisdevice 72 is a delaying network, which delays thefiy-back pulses fromthe device 39 for such a period that these pulses coincide in time withthe reference pulses contained in the output signals of the sistor isconnected on the side remote from the cathode to the positive terminalof a battery B1. The anode of the tube V is connected via a decouplingcapacitor C through the terminal K to the device 72, which thusfurnishes the fly-back pulses from the device 39, coinciding in timewith the reference signals contained in the signal applied to theterminal A. The voltage of the battery B1 is chosen to be so high thatthe tube V does not become conductive under the action of the signalapplied to the terminal A alone. It does become conductive, if the saiddelayed fly-back pulses occur at the anode, these pulses having asuitably chosen high voltage. This means that at the terminal D, duringthe occurrence of these fly-back pulses, also are produced pulsatorysignals, the amplitude of which is determined by the amplitude of thereference signals occurring at the input terminal A. By smoothing thepulses occurring at the terminal D a control-voltage is obtained, thevalue of which is determined by the level of the signals occurring atthe output of the amplifier 57 or 58. The control-Voltage occurring atthe output of the device 70, which thus comprises a gate circuit, is fedvia the smoothing network 73 to the amplifier 57, the amplificationfactor of which is controlled in accordance with the control-voltageconcerned in a manner similar to that of the aforesaid conventional gaincontrol, so that at an increasing value of the level of the signaloccurring at the output of the amplifier 57 the amplification factor ofthis amplifier decreases.

The output signal of the device 71 is fed via a smoothing network 74 toan amplifier 58, so that also the amplication factor of this amplifieris controlled in accordance with the control-voltage concerned.

In the foregoing it is always assumed that the reference signalsassociated with the signals modulated on the auxiliary carriers coincidein time. It will be obvious that this is not necessary. Then the twodevices 70 and 71 must be connected Via separate networks 72 havingdifferent delay times, to the device 39.

It should be noted here that with respect to the fact that the detectorcircuits and 56 are based on the conventional rectifier principle, `thefrequency of the auxiliary carrier on which the colour signal ismodulated and the frequency of the associated reference signal need notbe equal. In view of the purpose of the introduction ofnthereferencesignals the diiference between these twofrequencies-must, of course, notbe high.

Asfan example of a system according to the invention,

reference is made to a system in which a signal of large -bandwidth istransmitted continuously, whilst two other signals of smaller bandwidth,modulated on the same auxiliary carrier, are transmitted alternately.VIt will be obvious that in this case only one reference signal maysuffice.

:It should be noted that a control-voltage from the device 70 or 71 mayat the same time be used effectively for controlling the level of thesound signal. Use is preferably made to this end of the control-voltagederived from the reference signal which relatesto the auxiliary carrier,of which the frequency is nearest-the sound carrier.

,What is claimed is:

1. A transmission system for line-scanned television signals, comprisingsources of three color television signals, a main carrier wave modulatedby one of said color .television signals, a source of line synchronizingpulses,

each of said line synchronizing pulses having a back porch associatedtherewith, a source of at least two -aux- `iliary carrier waves ofdifferent frequencies and each modulated by a different one of theremaining two of -said three color television signals, means forgenerating having a constant amplitude and each having a, frequencysubstantiallyy thesame as that of the correspondingA auxiliary carrierwave, means for combining andvtransmitting said modulated carrier waves,said line synchronizing pulses and said reference signals, receiver-means for receiving said transmitted signals and comprising means forseparating the color signals vmodulated onsaid auxiliary carrier wavesfrom the received signals, a plurality of control means connected Vforrespectively controlling the amplitudes of said separated signalsinaccordance with the amplitudes of the respective reference signals,means for separating the signal modulated'on said -main carrier wavefrom the received signals, color picture display means, and means forapplying the three sadseparated signals to said color picture displaymeans.

2. A system as claimed in claim l, in which saidreference signalscoincide with respect to time.

3. A system as claimed in claim l, in Iwhich saidreceiver means includemeans for. producinga control pulse during each time of occurrence ofsaid back porches, and a plurality of gate circuits respectivelyconnected to said control means and responsive to said control pulsesfor causing said referencesignals yto actuate said control means.

Dome Apr. 14, 19.53 Larkey July 3l, 1956

